Fig 1: Prior iv BCG administration protects K18-hACE2 mice from lethal SARS-CoV-2 challenge.

(A-D) K18-hACE2 mice were inoculated with 10⁶ CFU BCG Pasteur by subcutaneous (sc) or intravenous (iv) injection. Control animals received the same volume of PBS iv. At 42 days post BCG administration, mice were infected with 10³ TCID₅₀ SARS-CoV-2 (WA1/2020) by intranasal instillation. (A) Schematic of experimental design. (B) Weight change following SARS-CoV-2 infection shown as percent of starting weight. (C) Animals were scored on a scale of 0–3 by a blinded observer, with 0 referring to no observable signs of disease and 3 referring to a moribund state requiring euthanasia. Scoring criteria are outlined in the Methods. (D) Kaplan-Meier curve of animal survival following SARS-CoV-2 challenge. Statistical significance was assessed by Mantel-Cox test. ns p>0.05; ****p<0.0001. Mean±SEM is shown. Data are pooled from 3 independent experiments each with 4–5 mice per group.